Communication systems compatible with TIA/EIA/IS-95-A, Mobile Station-Base Station Compatibility Standard for Dual Mode Wideband Spread Spectrum Cellular System, March 1995, published by the Electronic Industries Association (EIA), 2001 Eye Street, N.W., Washington, D.C. 20006, better known simply as IS-95, are well known. Recently, a feature has been included into IS-95-B, the next revision of the standard, which allows a mobile station to perform a handoff of the paging and access channel if it fails to receive an acknowledgment to access probes sent on an access channel. For example, the mobile station could begin sending access probes for a message on one access channel and then handoff to another paging/access channel to continue sending access probes of the message. The mobile station would then end the access attempt upon receiving an acknowledgment on the other paging channel. In IS-95-B, this feature is referred to as "access probe handoff."
One problem in adding this sort of handoff to IS-95-A is that, when using IS-95-A access channel messages to perform registration, it is not possible for the mobile station and base station to maintain synchronized registration variables. For example, a mobile station could begin sending a Registration Message to base station A in registration zone A, fail to receive acknowledgment to the message from base station A, perform a paging/access channel handoff to base station B in registration zone B, continue sending the message to base station B, and receive acknowledgment from base station B. (It should be noted that base station B may not have even received the access probe; the layer 2 (L2) acknowledgment on base station B could be "piggybacked" on another layer 3 (L3) message sent via both base stations A and B using the "access handoff" feature which has been included in IS-95B).
According to IS-95-A, the registration zone (as well as other registration variables, such as those for distance-based registration) in which the mobile station intended to register is implied to the infrastructure from the base station which received the access channel message. Because the mobile station cannot determine which base stations received the Registration Message, and because the infrastructure does not know where the mobile station intended to register, it is unclear to both the mobile station and the infrastructure how the registration variables should be updated. This same problem exists when implicit registration is performed in conjunction with "access probe handoff" using the Origination Message or the Page Response Message.
Thus, a need exists for a method and apparatus which overcomes the deficiencies of the prior art.